---
id: 06. Ethernet LAN Switching (part 2)
aliases: []
tags: []
---

# Ethernet LAN Switching (part 2)

## Ethernet Frame

- The preamble + SFD is usually not considered part of the Ethernet header
- therefore the size of the Ethernet header + trailer is 18 bytes (6+6+2+4)
- the minimum size for an Ethernet frame (Header + payload (Packet) + trailer) is 64 [[bytes]]
- 64 bytes - 18 bytes (header + trailer size) = 46 bytes
- therefore the minimum payload (packet) size is 46 bytes
- if the payload is less than 46 bytes, padding bytes are added
- ie. 34-byte packet + 12-byte padding = 46 bytes

## [[ARP]]

- ARP stands for 'Address Resolution Protocol'
- ARP is used to discover the Layer 2 address [[Mac address]] of a known Layer 3 address [[IP address]]
- Consists of two messages:
  - ARP Request
    - ARP Request is broadcast = sent to all hosts on the network
  - ARP Reply
    - ARP REply is unicast =  sent only to one host (the host that sent the request)

## ARP Table

- command to view the ARP table 
  - use *[[arp]] -a* ([[Windows]], [[macOS]], [[Linux]])
  - use *show arp* ([[Cisco]] devices)
- Internet Address = IP address (layer 3 address)
- Physical Address = MAC address (layer 2 address) 
- type static = default entry
- type dynamic = learned via ARP

## [[Ping]]

- A network utility that is used to test reachability
- Measures round-trip time
- Uses two messages
  - [[ICMP]] Echo Request
  - [[ICMP]] Echo Reply
- command to use pin: *ping (ip-address)*

## MAC address table

command to view it 
  - *show mac address-table*


```cisco
SW1#show mac address table

Vlan  Mac Address     Type    Ports
----  -----------     ----    -----
   1  0c2f.b011.9d00  DYNAMIC Gi0/0
   1  0c2f.b06a.3900  DYNAMIC Gi0/2

Total Mac addresses for this criterion: 2
```

- [[Vlan]] : Virtual local area network
- Ports = Interface

## Clearing the Mac address Table

for manually remove mac address table use this command
  - *clear mac address-table dynamic*
for just one mac address
  - *clear mac address-table dynamic address (mac address)*
  - *clear mac address-table dynamic address 0c2f.b06a.3900*
for one interface
  - *clear mac address-table dynamic interface (interface)*
  - *clear mac address-table dynamic interface Gi0/0*

## Summary
- Ethernet frame payload minimum size
- ARP (Address Resolution Protocol)
  - ARP Request 
  - ARP Reply 
- ARP table
- Ping
  - ICMP Echo Request
  - ICMP Echo Reply
- Mac Address Table